The present invention is directed to a pressure relief valve utilized particularly on fuel delivery tank trucks to relieve the internal pressure developed within the tank in the event of a rollover or other accident in which the tank wall may be deformed in a manner reducing its internal volume.
When a fuel delivery truck is involved in an accident, spillage of fuel from its tanks normally results in a massive fire. In severe accidents, rupture or puncture of one or more of the storage compartments of the tank cannot be avoided. However, in those somewhat less severe accidents where the tank wall is not punctured, but is deformed in a manner decreasing its internal volume, rupture of the tank wall by the increased internal pressure can be avoided by venting the interior of the tank to relieve the pressure. Relief valves for accomplishing this purpose have been employed in the prior art, however, the prior art valves are so constructed that in venting the tank to relieve the internal pressure, a certain quantity of fuel is also vented and spilled. Presently proposed regulations will require that vent valves of this type operate in a manner such that no fuel at all is spilled during the venting operation.
The present invention is directed to a rollover or pressure relief valve which will meet this last requirement.